Transistor ignition system with ballast compensation

ABSTRACT

An ignition system has a transistor connected in series with a primary winding of a conventional spark coil, and a sensing resistor is also connected in series with the transistor. A silicon-controlled rectifier has the anode thereof connected to the base electrode of the transistor and the cathode thereof coupled to the emitter of the transistor effectively to be in parallel with the base-emitter junction. The gate electrode of the silicon-controlled rectifier is coupled to the sensing resistor to be rendered conductive in response to a predetermined voltage level developed at the sensing resistor. The siliconcontrolled rectifier, when conductive, decreases the current flow through the transistor and the primary winding of the spark coil and, when nonconductive, increases the current flow through the transistor and the primary winding of the spark coil.

United States Patent Gunther Schuette [72] Inventor Addison, Ill. [211 App]. No. 41,489 [22] Filed May 28, 1970 [45] Patented Aug. 17, 1971 [73] Assignee Motorola, Inc.

Franklin Park, Ill.

[54] I TRANSISTOR IGNITION SYSTEM WITH BALLAST COMPENSATION 8 Claims, 1 Drawing Fig.

[52] U.S. Cl 123/148 E, 315/209 [51 1. Int. Cl 1105b 37/02,- 1105b 39/04, F02p 1/00 [50] Field of Search 123/148 C; 315/209 [56] References Cited I UNITED STATES PATENTS 3,072,823 1/1963 Kirk 123/148 3,078,391 2/1963 Bundodiere 123/148 3,152,281 10/1964 Robbins 1.

Primary Examiner-Mark M. Newman Assistant Examiner-Ronald B. CoX Attorney-Mueller and Aichele ABSTRACT: An ignition system has a transistor connected in series with a primary winding of a conventional spark coil, and a sensing resistor is also connected in series with the transistor. A silicon-controlled rectifier has the anode thereof connected to the base electrode of the transistor and the cathode thereof coupled to the emitter of the transistor effectively to be in parallel with the base-emitter junction. The gate electrode of the silicon-controlled rectifier is coupled to the sensing resistor to be rendered conductive in response to a predetermined voltage level developed at the sensing resistor. The silicon-controlled rectifier, when conductive, decreases the current flow through the transistor and the primary winding of the spark coil and, when nonconductive, increases the current flow through the transistor and the primary winding of the spark coil.

BACKGROUND OF THE INVENTION This invention relates generally to a transistor ignition system and moreparticularly to a transistor ignition system I useable with the standard ignition coil of an automobile.

Heretofore, transistor ignition systems have been provided which allow for use of the standard ignition coil. However, these transistor ignition systems generally provide means only for increasing breaker point life without actually enhancing the fuel-igniting properties of the spark produced thereby. A ballast resistor may be connected in series with the ignition coil to limit the current flow therethrough. However, these prior art ignition systems generally required that the ballast resistor associated with some automobiles be removed from the circuit and in some cases, required that a ballast resistor, if not already provided, be added, depending upon the type of transistor ignition system used.

Several transistor ignition systems have been provided which utilize a special ignition coil having a fewer number of turns in the primary winding thereof to allow for a substantially increased current flow during conduction of the transistor. However, this type of ignition system is more expensive in that the standard ignition coil must be replaced with the special ignition coil having the fewer number of turns in the primary winding.

SUMMARY OF THE lNVENTlON Accordingly, it is an object of this invention to provide a transistor ignition system which can be used in conjunction with the standard ignition coil ol'an automobile.

Another object of this invention is to provide a transistor ignition, system which will function properly regardless-of whether 'or not a ballast resistor is connected in series therewith, thus eliminating the need of concern of adding or removing a ballast resistor within an automobile ignition system.

'A feature of this invention is the use of a silicon-controlled rectifier connected so as to form a shunt current path with the base-emitter junction of the transistor of the ignition system. This will provideeither a maximum current flow through the transistor, when the silicon-controlled rectifier is in its nonconductive state, or a reduced current flow through the transistor, when the silicon-controlled rectifieris in its conductive state.

DESCRIPTION OF THE PREFERRED EMBODIMENT The single FIGURE illustrates a schematic diagram of a transistor ignition system constructed in accordance with the principals of this'invention. Here the battery of an automobile is designated generally by reference numeral and provides an operating potential to the transistor ignition system. Also, an alternator charging circuit may be incorporated although'it is not shown herein. An ignition switch 12 is provided to apply potential to the primary winding 14a ofa standard ignition coil 14, the secondary winding 14b thereof being arranged to apply spark discharges to an internal combustion engine in any usual and well-known manner. In the illustrated embodiment, a ballast resistor I6 forms part of the ignition system of an automobile into which the ignition system of this invention is inserted. However, it will be understood that the resistor 16 may be eliminated. The ballast resistor 16 is a low-resistance, highwattage element provided to reduce the current flow through the primary winding 14a. ln many cases, when installing a transistor ignition system, it is this ballast resistor that is to be removed or bypassed. To prevent the wrong polarity of voltage from being applied to the transistor ignition system, a blocking diode 18 has the anode thereof connected to the resistor16 and the cathode thereof connected to the primary winding 14a.

The ignition system of this invention consists primarily of those components illustrated in the broken line area designated by reference numeral 20. Here a transistor 22 has the collector-emitter junction thereof connected in series with the primary winding 14a and in series with a sensing resistor 24. Upon conduction of transistor 22, a voltage drop is developed across resistor 24 and applied to the gate electrode of a silicon-controlled rectifier 26. However, the silicon-controlled rectifier is rendered conductive only when the voltage across resistor 24 reaches a predetermined level. The anode of the silicon-controlled rectifier is connected to a circuit point 28 which, in turn, is connected to the base electrode of transistor 22 effectively to control the amount of control current passing through the base-emitter junction of the transistor 22. A current-limiting resistor 30 is connected between the gate electrode of silicon-controlled rectifier 26 and a junction point between the emitter of transistor 22 and sensing resistor 24. Also, a resistor 32 is connected in series with the siliconcontrolled rectifier 26 to provide a predetermined voltage drop upon conduction of the silicon-controlled rectifier, which voltage drop then provides a new bias condition across thebase-emitter junction of transistor 22 effectively to reduce the amount of current flow through the transistor. A temperature-responsive transistor 34 is connected to the gate electrode of silicon-controlled rectifier 26 to stabilize the voltage condition required at the gate electrode of the silicon-controlled rectifier to render it conductive. A diode 38 is connected between the base-emitter junction of transistor 22 to protect the transistor from inadvertent reverse voltage conditions which may occur.

Therefore, transistor 22 has two effective conductive conditions, one conductive condition being maximum when siliconcontrolled rectifier 26 is nonconductive and the other conductive condition being somewhat reduced when silicon-controlled rectificr 26 is conductive.

The electrical characteristic of the primary winding 14a, together with the sensing resistor 24, will cause a decreased voltage condition to exist across the sensing resistor 24 at high engine r.p.m. This decreased voltage condition will render silicon-controlled rectifier 26 nonconductive, if is was previously conductive as would be the case where ballast resistor 16 is eliminated from the circuit, to increase the current through transistor 22 which, in turn, will increase the current through primary winding 14a and produce a substantial increase in the fuel-igniting properties of a spark produced at the output of the transformer 14.

A conventional breaker point arrangement 40, as is well known in the art, has one contactor thereof connected to ground potential and the other contactor thereof coupled to the base electrode of a transistor 42 through a resistor 44. The resistor 42 is a current gain device and has the emitter-collector junction thereof connected in series with the base-emitter junction of transistor 22 through a resistor 46. Although a conventional breaker point arrangement is illustrated herein, it will be understood that any suitable means to provide external pulse signal information to the transistor ignition system may be incorporated. 4

To stabilize the collector electrode of transistor 22. a capacitor 50 and a voltage-dependent resistor 52 are connected thereto as a filter. The voltage-dependent resistor 52 has one end thereof connected to the juncture of transistor 22 and primary winding 14a and the other end thereof connected to ground potential. On the other hand, capacitor 50 has one end thereof connected to the juncture between transistor 22 and primary winding with the other end thereof con nected to the battery supply 10.

The operation of the transistor ignition system at low r.p.m. when the ballast resistor 16 is absent is that the silicon-controlled rectifier 26 will conduct, due to increased voltage across resistor 24, to shunt the base of transistor 22 and change the bias on the transistor so that the current flow therethrough will be reduced. However, at high rpm. the voltage sensed across resistor 24 will decrease because of the through transistor 22 and enhance the fuel-igniting properties of the spark produced at the output of the ignition coil 14 to improve high-speed performance of the engine.

Where the ballast resistor 16 is present, as may be the case where a high-resistance wire is used within the ignition wiring of an automobile, the'voltage drop across resistor 24 will be insufficient to render silicon-controlled rectifier 26 conductive.- This action will cause maximum current flow to pass through transistor 22 at all times.

Accordingly, what has been described is a transistor ignition system which operates effectively with the standard ignition coil of an automobile and which can be used with or without a ballast resistor connected in series therewith without the need of removing or adding such resistor. lt will be understood, therefore, that variations and modifications of this invention may be effected without departing from the spirit and scope of the novel concepts disclosed and claimed herein.

I claim: I. A transistor ignition system for fuel combustion engines,

including in combination:

switch means responsive to the rotation of the engine to provide control current;

a coil having a primary winding arranged for connection to a voltage source;

a first current control device connected with said primary winding to control current flow therethrough and having a control electrode coupled to said switch means to receive said control current to cause conduction of said first current control device; and

a second current control device connected to said control electrode of said first current control device to vary the control current applied to said first current control device upon a first conductive state of said second current control device to decrease current flow through said primary winding, and to allow full control current flow to said first current control device upon a second conductive state of 5 said second current control device to increase current flow through said primary winding.

2. The transistor ignition system of claim 1 wherein said first current control device is a transistor having the emitter-collector junction thereof connected in series with said primary winding, said control electrode being the base electrode of said transistor, and said second current control device is a silicon-controlled rectifier having the anode-cathode junction thereof connected in parallel with the base-emitter junction of said transistor with the gate electrode of said silicon-controlled rectifier coupled to said transistor to sense current flow therethrough.

3. The transistor ignition system of claim 1 further including a sensing resistor connected in series with said first current control device, and said control electrode of said second current control device is coupled to said sensing resistor to render said second current control device conductive in response to a predetermined voltage value developed across said sensing resistor. I

4. The transistor ignition system of claim 3 wherein the re-' sistance value of said sensing resistor and the reactance value of said primary winding cause a decreasing voltage across said sensing resistor with increased r.p.m. of said fuel combustion engine to disable said second current control device.

5. The transistor ignition system of claim 1 further including a ballast resistance means connected in series with said primary winding and said first current control device.

6. The transistor ignition system of claim 1 further including a third current control device having load electrodes connected in series between a power source and the junction of the control electrode of said first current control device and a given load electrode of said second current control device, said third current control device having a control electrode coupled to said switch means to be rendered conductive in res onse thereto.

. A transistor ignition system for operating from a voltage source including in combination:

an ignition coil having a primary winding with one end thereof connected to the voltage source and a secondary winding arranged to supply spark discharges;

a transistor having the emitter-collector junction thereof connected in series with said primary winding and further having a base electrode;

a sensing resistor connected in series with the emitter-collector junction of said transistor to develop a voltage thereacross indicative of the conductive state of said transistor;

switch means to develop external pulse signal information, said switch means coupled to said base electrode of said transistor periodically to render said transistor conductive thus energizing said primary winding; and

a silicon-controlled rectifier having the anode-cathode junction thereof connected in parallel with the base-emitter junction of said transistor and the gate electrode of said silicon-controlled rectifier coupled to said sensing resistor to render said silicon-controlled rectifier conductive in response to a predetermined voltage value at said sensing resistor.

8. The transistor ignition system of claim 7 further including a ballast resistance means connected in series with said primary winding and said transistor. 

2. The transistor ignition system of claim 1 wherein said first current control device is a transistor having the emitter-collector junction thereof connected in series with said primary winding, said control electrode being the base electrode of said transistor, and said second current control device is a silicon-controllEd rectifier having the anode-cathode junction thereof connected in parallel with the base-emitter junction of said transistor with the gate electrode of said silicon-controlled rectifier coupled to said transistor to sense current flow therethrough.
 3. The transistor ignition system of claim 1 further including a sensing resistor connected in series with said first current control device, and said control electrode of said second current control device is coupled to said sensing resistor to render said second current control device conductive in response to a predetermined voltage value developed across said sensing resistor.
 4. The transistor ignition system of claim 3 wherein the resistance value of said sensing resistor and the reactance value of said primary winding cause a decreasing voltage across said sensing resistor with increased r.p.m. of said fuel combustion engine to disable said second current control device.
 5. The transistor ignition system of claim 1 further including a ballast resistance means connected in series with said primary winding and said first current control device.
 6. The transistor ignition system of claim 1 further including a third current control device having load electrodes connected in series between a power source and the junction of the control electrode of said first current control device and a given load electrode of said second current control device, said third current control device having a control electrode coupled to said switch means to be rendered conductive in response thereto.
 7. A transistor ignition system for operating from a voltage source including in combination: an ignition coil having a primary winding with one end thereof connected to the voltage source and a secondary winding arranged to supply spark discharges; a transistor having the emitter-collector junction thereof connected in series with said primary winding and further having a base electrode; a sensing resistor connected in series with the emitter-collector junction of said transistor to develop a voltage thereacross indicative of the conductive state of said transistor; switch means to develop external pulse signal information, said switch means coupled to said base electrode of said transistor periodically to render said transistor conductive thus energizing said primary winding; and a silicon-controlled rectifier having the anode-cathode junction thereof connected in parallel with the base-emitter junction of said transistor and the gate electrode of said silicon-controlled rectifier coupled to said sensing resistor to render said silicon-controlled rectifier conductive in response to a predetermined voltage value at said sensing resistor.
 8. The transistor ignition system of claim 7 further including a ballast resistance means connected in series with said primary winding and said transistor. 